An orchestrated campaign is being waged against climate change science to undermine public acceptance of man-made global warming, environment experts claimed last night.

The attack against scientists supportive of the idea of man-made climate change has grown in ferocity since the leak of thousands of documents on the subject from the University of East Anglia (UEA) on the eve of the Copenhagen climate summit last December.

Free-market, anti-climate change think-tanks such as the Atlas Economic Research Foundation in the US and the International Policy Network in the UK have received grants totalling hundreds of thousands of pounds from the multinational energy company ExxonMobil. Both organisations have funded international seminars pulling together climate change deniers from across the globe.

Many of these critics have broadcast material from the leaked UEA emails to undermine climate change predictions and to highlight errors in claims that the Himalayan glaciers could disappear by 2035. Professor Phil Jones, who has temporarily stood down as director of UEA's climactic research unit, is reported in today's Sunday Times to have "several times" considered suicide. He also drew parallels between his case and that of Dr David Kelly, found dead in the wake of the row over the alleged "sexing up" of intelligence in the run-up to the invasion of Iraq. Professor Jones said he was taking sleeping pills and beta-blockers and had received two death threats in the past week alone.

Climate sceptic bloggers broadcast stories last week casting doubts on scientific data predicting dramatic loss of the Amazon rainforest. All three stories, picked up by mainstream media, questioned the credibility of the International Panel on Climate Change (IPCC) and the way it does its work. A new attack on climate science, already dubbed "Seagate" by sceptics, relating to claims that more than half the Netherlands is in danger of being submerged under rising sea levels, is likely to be at the centre of the newest skirmish in coming weeks.

The controversies have shaken the IPCC, whose chairman, Dr Rajendra Pachauri, was subjected to a series of personal attacks on his reputation and lifestyle last week. A poll this weekend confirmed that public confidence in the climate change consensus has been shaken: one in four Britons – 25 per cent – now say they do not believe in global warming; previously this figure stood at 15 per cent.

Professor Bob Watson, the chief scientific adviser to the Department for Environment, Food and Rural Affairs (Defra) and former chairman of the IPCC, said yesterday that the backlash is the result of a campaign: "It does appear that there's a concerted effort by a number of sceptics to undermine the credibility of the evidence behind human-induced climate change." He added: "I am sure there are some sceptics who may well be funded by the private sector to try to cast uncertainty."

A complicated web of relationships revolves around a number of right-wing think-tanks around the world that dispute the threats of climate change. ExxonMobil is a key player behind the scenes, having donated hundreds of thousands of dollars in the past few years to climate change sceptics. The Atlas Foundation, created by the late Sir Anthony Fisher (founder of the Institute of Economic Affairs), received more than $100,000 in 2008 from ExxonMobil, according to the oil company's reports.

Atlas has supported more than 30 other foreign think-tanks that espouse climate change scepticism, and co-sponsored a meeting of the world's leading climate sceptics in New York last March. Called "Global Warming: Was It Ever Really a Crisis?", it was organised by the Heartland Institute – a group that described the event as "the world's largest-ever gathering of global warming sceptics". The organisation is another right-wing think-tank to have benefited from funding given by ExxonMobil in recent years.

A large British contingent was present at the event, with speakers including Dr Benny Peiser, from Lord Lawson's climate sceptic think-tank, the Global Warming Policy Foundation (GWPF); the botanist David Bellamy; Julian Morris and Kendra Okonski from the London-based International Policy Network; the weather forecaster Piers Corbyn; Christopher Monckton, a former policy adviser to Margaret Thatcher; and Professor David Henderson, a member of GWPF's advisory council. Speakers at the event also included two prominent climate bloggers who associate with Paul Dennis, a 54-year-old climate researcher at the University of East Anglia who has been questioned by police investigating the theft of climate data.

In a posting on the blog of the climate sceptic Andrew Montford on Friday, Mr Dennis insisted: "I did not leak any files, data, emails or any other material. I have no idea how the files were released or who was behind it."

But he confirmed that he had been in email contact with Stephen McIntyre, who runs climateaudit.org – a site that was one of the first to receive an anonymous link to the original leaked data from UEA.

Mr Dennis said he emailed Mr McIntyre to alert him to a "departmental email saying that emails and files were hacked" and that "police had copies of my email correspondence with Steve McIntyre and Jeff Id [a pseudonym for the climate sceptic Patrick Condon]. They said it was because I had sent the emails that they were interviewing me."

The UEA researcher also has connections with another prominent sceptic, Anthony Watts, with whom he has posted and who spoke beside Mr McIntyre. Mr Dennis was not available for comment.

Bob Ward, the policy director of the Grantham Research Institute on Climate Change at the London School of Economics, said: "A lot of the climate sceptic arguments are being made by people with demonstrable right-wing ideology which is based on opposition to any environmental regulation of the market, and they are clearly being given money that allows them to disseminate their views more widely than would be the case if they didn't have oil company funding."

But Dr Richard North, a climate change sceptic and blogger, rejected claims of a conspiracy as "laughable" and denied having any links to vested interests. "Anybody who knows me knows I'm a loner. Nobody tells me what to do or dictates my agenda."

ExxonMobil said in a statement: "We have the same concerns as people everywhere – and that is how to provide the world with the energy it needs while reducing greenhouse gas emissions."